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Letter 4200

Darwin, C. R. to Gosse, P. H.

2 June [1863]

    Summary Add

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    Can only conjecture that the problem occurs because the plant is not living in its natural conditions. Refers to what he said on Acropera [in Orchids]. Many plants under culture have sexual functions altered.

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    Asks PHG to look at bee Ophrys at Torquay to see if pollinia are ever removed. "It is my greatest puzzle."

Transcription

Down. | Bromley. | Kent. S.E.

June 2d

My dear Sir

It would give me real pleasure to resolve your doubts, but I cannot. I can give only suspicions & my grounds for them. I should think the non-viscidity of the stigmatic hollow was due to the plant not living under its natural conditions. Please see what I have said on Acropera; an excellent observer Mr. J. Scott of Bot. Garden Edinburgh finds all that I say accurate, but nothing daunted he with the knife enlarged orifice & forced in pollen-masses; or he simply stuck them into the contracted orifice without coming into contact with the stigmatic surface, which is hardly at all viscid; when lo & behold pollen-tubes were emitted & fine seed capsules obtained. This was effected with Acropera Loddigesii; but I have no doubt that I have blundered badly about A. luteola. I mention all this because as Mr Scott remarks, as the plant is in our Hot-House it is quite incredible it ever could be fertilised in its native land. The whole case is an utter enigma to me.—

Probably you are aware that there are cases (& it is one of the oddest facts in physiology) of plants which under culture have their sexual functions in so strange a condition, that though their pollen & ovules are in sound state & can fertilise & be fertilised by distinct but allied species; they cannot fertilise themselves. Now Mr Scott has found this the case with certain Orchids, which again shows sexual disturbance. He has read paper at Bot. Soc. of Edinburgh & I daresay an abstract which I have seen will appear in Gard. Chron; but blunders have crept in in copying & parts are barely intelligible. How insects act with your Stanhopea, I will not pretend to conjecture. In many cases, I believe the acutest man could not conjecture without seeing the insect at work. I could name common English plants in this predicament.— But the Musk orchis is case in point. Since publishing my son & self have watched the plant & seen the pollinia removed & where do you think they invariably adhere in dozens of specimens; always to the joint of femur with the trochanter of 1st. pair of legs & no where else. When one sees such adaptation as this, it would be hopeless to conjecture on the Stanhopea till we know what insect visits it. I have fully proved that my strong suspicion was correct that with many of our English orchids no nectar is excreted, but that insects penetrate the tissues for it. So I suspect it must be with many foreign species.

I forgot to say, that if you find you cannot fertilise any of your exotics take pollen from some allied form & it is quite probable that will succeed.—

Will you have the kindness to look occasionally at your Bee Ophrys near Torquay & see whether pollinia are ever removed. It is my greatest puzzle. Please read what I have said on it & on O. arachnites; I have since proved account of latter is correct. I wish I could have given you better information.

My dear Sir | Yours sincerely | Ch. Darwin

P.S. | If the flowers of the Stanhopea are not too old—remove pollen-masses from their pedicels & stick them with a little liquid pure gum to stigmatic cavity. After the case of the Acropera, no one can dare positively say that they would not act.—

    Footnotes Add

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    f1 4200.f1
    The year is established by the relationship between this letter and the letter from P. H. Gosse, 30 May 1863.
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    f2 4200.f2
    In his letter to CD of 30 May 1863, Gosse described the difficulties he had experienced in attempting to pollinate the orchid Stanhopea oculata, noting in particular that what he assumed to be the stigma was not viscous, so that pollinia would not adhere to it.
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    f3 4200.f3
    CD described the floral morphology of the orchid genus Acropera in Orchids, pp. 204--10, noting that, in the specimens he had seen, the orifice of the stigmatic chamber was so narrow that the pollen-masses could `hardly be forced in' (p. 205). As with Gosse's Stanhopea, CD considered the possibility that this may have been due to unnatural conditions, but concluded that his experience of orchids grown in hothouses furnished `no reason' to believe this to be the case (p. 209).
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    f4 4200.f4
    See, for example, Correspondence vol. 10, letter from John Scott, 11 November 1862, and this volume, letter from John Scott, 18 February [1863]. John Scott was foreman of the propagating department at the Royal Botanic Garden, Edinburgh (R. Desmond 1994).
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    f5 4200.f5
    In Orchids, p. 203 n., CD reported that Acropera luteola differed `in little or in nothing from A. Loddigesii', and that it might be a variety of the same species. CD refers to his conclusion that there was a separation of the sexes in A. luteola (see Orchids, pp. 206--9), which he later described as `a great error', Scott's results having convinced him that the species of this genus were hermaphrodite (see `Fertilization of orchids', p. 153 (Collected papers 2: 150)).
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    f6 4200.f6
    In his letter to CD of [after 12] April [1863], Scott made an observation of this nature with respect to orchids of the genus Gongora, which had also been found to have a stigmatic chamber with a narrow orifice.
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    f7 4200.f7
    Before he concluded that there was separation of the sexes in Acropera, CD had considered the genus to be the `opprobrium' of his work on the pollination mechanisms of orchids, since all the floral parts `seemed determinately contrived that the plant should never be fertilised' (Orchids, p. 203). For CD's subsequent explanation of his observations, see the letter to Friedrich Hildebrand, 28 July [1863], and `Fertilization of orchids', p. 153 (Collected papers 2: 150).
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    f8 4200.f8
    CD described cases of this sort in Origin, pp. 250--1.
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    f9 4200.f9
    CD refers to Scott 1863a, which was read before the Botanical Society of Edinburgh on 14 May 1863. An abstract of the paper was published in the Edinburgh Evening Courant, 28 May 1863, p. 8; Scott enclosed a corrected copy of the abstract with his letter to CD of 28 May [1863]. The abstract was also published in the Gardeners' Chronicle, 13 June 1863, p. 558.
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    f10 4200.f10
    CD refers to George Howard Darwin's observations of Herminium monorchis, made between 22 and 27 June 1862 (see CD's notes in DAR 70: 32--6), and later published in the German translation of Orchids (Bronn trans. 1862, pp. 47--8 n.) and `Fertilization of orchids', pp. 145--6 (Collected papers 2: 142--3). Orchids was published in May 1862 (Freeman 1977, p. 112).
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    f11 4200.f11
    In Orchids, pp. 44--53, CD described the apparent failure of several species of Orchis to produce nectar, despite possessing nectaries. CD's hypothesis was that these plants did produce nectar, but secreted it into the intercellular spaces between the inner and outer membranes of the nectary, an arrangement requiring insects to spend more time in the flower in order to extract the nectar by boring through the inner membrane of the nectary. While staying at Hartfield Grove, Hartfield, Sussex, in May 1863, CD made additional observations of the nectaries of Orchis morio and O. maculata, and of the behaviour of insects visiting the flowers, which confirmed his earlier conclusions (see `Fertilization of orchids', pp. 142--3 (Collected papers 2: 140), and the dated observational notes in DAR 70: 176--7). See also letter to John Scott, 2 May [1863] and n. 15.
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    f12 4200.f12
    CD described the bee ophrys (Ophrys apifera) in Orchids, pp. 63--72, stating that he found the case `perplexing in an unparalleled degree', since the flowers appeared to have `elaborate contrivances for directly opposed objects', that is, adaptations for both cross- and self-fertilisation. One of CD's objectives in Orchids was to demonstrate that cross-fertilisation was the `main object' of the `contrivances' by which orchids were pollinated (Orchids, p. 1), noting in his conclusion to the book that O. apifera was the only species in which he had observed `special and perfectly efficient contrivances for self-fertilisation' (Orchids, p. 359). CD had carried out extensive but inconclusive observations designed to establish whether the pollinia were ever removed by insects in this species (Orchids, pp. 66--70). Gosse lived at Babbacombe Bay, near Torquay, Devon, where CD had made some of these observations (Orchids, p. 66).
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    f13 4200.f13
    In Orchids, pp. 72--3, CD noted that many botanists considered Ophrys arachnites to be a `mere variety' of O. apifera; however, having observed that there was no adaptation for self-pollination in O. arachnites, CD argued that it should be considered a `good species'.
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    f14 4200.f14
    Following the publication of Orchids in May 1862, CD continued to be interested in the functional differences between Ophrys apifera and O. arachnites (see Correspondence vol. 10). CD reported his additional observations on O. arachnites in `Fertilization of orchids', p. 145 (Collected papers 2: 142).
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